1. Technical Field
This invention relates generally to an apparatus and method for microelectronics fabrication. More specifically, the invention relates to methods for controlling the mix ratio of an etching chemical used for etching microcircuit linewidths that are patterned on semiconductor wafers.
2. Description of the Prior Art
The following document relates to methods dealing with wet etching for VLSI.
"Silicon Processing for the VLSI Era" Vol. 1, Process Technology by Stanley Wolf et al, Published by Lattice Press, Sunset Beach, Calif. in 1986, pp. 520-523 and 529-534 describing wet etch processing using various etching chemicals including HF.
The manufacture of an integrated circuit device requires the formation of various layers (both conductive and non-conductive) above a substrate to form the necessary components and interconnects. During the manufacturing process, certain layers or portions of layers must be removed in order to pattern and form the various components and interconnects. Etching in microelectronics fabrication is a process by which material is removed from the semiconductor wafer or thin films on the wafer surface. During the photolithographic process, a mask layer is used to protect specific regions of the wafer surface, the goal of etching is to precisely remove the material which is not covered by the mask.
Several etching processes are used for microelectronics fabrication. In-Situ sputter etch for oxide removal, and wet etch for patterning of linewidths. This invention is concerned with improvements to the wet etching process.
Wet etching processes are generally isotropic. As such, they are inadequate for defining features less than about 3 .mu.m wide. Nevertheless, for those process that involve patterning of linewidths greater than 3 .mu.m, wet etching continues to be a viable technology. Since it turns out that a significant fraction of semiconductor products are still being fabricated with such geometries, wet etching should not be ignored.
The reason wet etching has found widespread acceptance in microelectronic fabrication is that it is a low cost, reliable, high throughput process with excellent selectivity for most wet etch processes, with respect to both mask and substrate materials. Wet etching of SiO.sub.2 films in microelectronic applications is usually accomplished with various hydrofluoric acid (HF) solutions. This is because silicon dioxide is readily attacked by room temperature HF, while silicon is not. Etching takes place according to the overall reaction: SiO.sub.2 +6HF&gt;H.sub.2 +Si F.sub.6 +2 H.sub.2 O.